In recent years, a personal communication device has been miniaturized and diversified significantly with a field of personal communication rapidly developed. Various data services, such as multimedia information, online gaming, video-on-demand, music download, and mobile TV, have been provided and personal demand for communication and entertainment seems to be substantially satisfied with them. Under the circumstances, a main problem of a next-generation mobile communication system would be how to provide a user with a higher peak velocity and a wider system frequency band.
At the 53rd meeting of 3GPP RAN1, held in Kansas City in the U.S. on May 5-9, 2008, by 3GPP (the 3rd Generation Partner Project) which is an international organization for standardization, requirements for LTE-Advanced and possible propositions related to the LTE-Advanced were discussed. After the meeting, “TR36.913v8.0.0, Requirements for Further Advancements for E-UTRA (LTE-Advanced)” was submitted and adopted, in which it is clearly stated that the LTE-Advanced system having a maximum system frequency band of 100 MHz should be supported. In addition, a great number of companies proposed, at the meeting, that an uplink system bandwidth narrower than a downlink system bandwidth should be supported (see Non Patent Literature 1, for example).
This proposition, however, gives rise to a problem that the uplink system bandwidth and the downlink system bandwidth of the LTE-Advanced system would be different in size from each other. As to a conventional LTE system, the uplink system bandwidth and the downlink system bandwidth are equal in size to each other, and the maximum system bandwidth is 20 MHz. The conventional LTE system has thus allowed its LTE base station to accurately acquire, from an LTE user device (mobile station terminal), uplink control signaling in a downlink bandwidth occupied by the LTE user device (i.e. downlink control signaling related to uplink control information, also called “DCI (Downlink Control Information) format 0”). In contrast, the LTE-Advanced system employs the uplink system bandwidth and the downlink system bandwidth which are asymmetric to each other. Thus, it has been required a novel method for feeding back the uplink control signaling to the base station.
Further, one of the above requirements for the LTE-Advanced is compatibility between the LTE-Advanced system and a conventional LTE user device, that is, operation of LTE and LTE-Advanced should be possible in the same frequency spectrum.